hvac - How to Sync Booster Fan with Furnace Fan - Home ...
1. This answer is not useful. Show activity on this post. Using a 24v/110v relay (installed in the booster fan's junction box) run 2-conductor T-stat wire back to your furnace. hook 1 conductor to ground, and hook the other conductor to your T-stat's fan wire (usually green, but whatever wire is connected to the "G" terminal on your T-stat).